In a mobile communication system, a user equipment (UE) may receive information from a base station (eNB) in downlink, and the UE may transmit information in uplink. The information which may be transmitted or received by the UE includes data and a variety of control information. There are various physical channels depending on the kind and use of information transmitted or received by the UE.
FIG. 1 is a view showing physical channels used for a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, which is an example of a mobile communication system, and a general signal transmission method using the same.
When a UE is powered on or when the UE newly enters a cell, the UE performs an initial cell search operation such as synchronization with an eNB in step S101. To this end, the UE may receive a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) from the base station so as to perform synchronization with the eNB, and acquire information such as a cell ID. Thereafter, the UE may receive a physical broadcast channel from the eNB and acquire broadcast information in the cell. Meanwhile, the UE may receive a Downlink Reference signal (DL RS) in the initial cell search step and confirm a downlink channel state.
The UE which completes the initial cell search may receive a Physical Downlink Control Channel (PDCCH) and a Physical Downlink Shared Channel (PDSCH) corresponding to the PDCCH, and acquire more detailed system information in step S102.
Meanwhile, the UE which does not complete the access to the eNB may perform a random access procedure in steps S103 to S106, in order to complete the access to the eNB. To this end, the UE may transmit a feature sequence via a Physical Random Access Channel (PRACH) as a preamble (S103), and may receive a message in response to the random access procedure via the PDCCH and the PDSCH corresponding thereto (S104). In contention-based random access except for handover, a contention resolution procedure including the transmission of an additional PRACH (S105) and the reception of the PDCCH and the PDSCH corresponding thereto (S106) may be performed.
The UE which performs the above-described procedure may then receive the PDCCH/PDSCH (S107) and transmit a Physical Uplink Shared Channel (PUSCH)/Physical Uplink Control Channel (PUCCH) (S108), as a general uplink/downlink signal transmission procedure.
Meanwhile, if several pieces of transmission information are received, for example, if Multiple-Input Multiple-Output (MIMO) technology, multiuser detection technology or multi-code technology is used, it is possible to improve performance using an interference cancellation type receiver.
In an interference cancellation scheme such as a Successive Interference Cancellation (SIC) scheme, first information out of an overall received signal including several pieces of information is demodulated/decoded, information associated with the first information is removed from the overall received signal, a second signal out of the signal in which the first information is removed from the overall received signal is demodulated/decoded, a third signal out of the signal in which the first information and the second information are removed from the first received signal is demodulated/decoded, and the above-described process is performed with respect to a fourth signal and the subsequent signals thereof. By successively removing the demodulated/decoded signals from the received signal, it is possible to improve the performance of the subsequent demodulating/decoding process.
Meanwhile, if a signal is transmitted using a MIMO scheme, the transmitted signal is transmitted in the layer units. Accordingly, error detection of the layer units is required for efficiently implementing the above-described SIC scheme, and in depth research thereinto is required.